Abstract:

A system and method for conditioning the temperature of at least one fluid
stream that is passed through a fuel cell stack is provided. The system
comprises a system module, at least one inlet and a conditioning device.
The system module is operable to humidify the fluid stream to a reach a
predetermined humidity level that corresponds to a predetermined
temperature. The one inlet of the fuel cell stack receives the fluid
stream at a first temperature that is different from the predetermined
temperature. The fuel cell stack includes at least one outlet operable to
present coolant having a temperature that is different from the first
temperature of the fluid stream. The conditioning device is operable to
receive the fluid stream and the coolant and present the fluid stream to
the coolant to change the first temperature of the fluid stream to be
equal to the predetermined temperature.

Claims:

1. A system for conditioning the temperature of at least one fluid stream
that is passed through a fuel cell stack, the system comprising:a system
module disposed upstream of the fuel cell stack and operable to humidify
the fluid stream so that the fluid stream reaches a predetermined
humidity level and the predetermined humidity level corresponds to a
predetermined temperature;at least one inlet of the fuel cell stack
adapted to receive the fluid stream at a first temperature that is
different from the predetermined temperature, the fuel cell stack having
at least one outlet that is operable to present coolant having a
temperature that is different from the first temperature of the fluid
stream in response to receiving the fluid stream; anda conditioning
device operable to receive the fluid stream and the coolant and present
the coolant to the fluid stream to change the first temperature of the
fluid stream to be equal to the predetermined temperature so that the
inlet of the fuel cell stack receives the fluid stream at the
predetermined temperature.

2. The system of claim 1 further comprising at least one temperature
sensor disposed on the conditioning device and operable to measure the
first temperature of the fluid stream and generate a first signal that
corresponds to the measured first temperature.

3. The system of claim 2 further comprising a controller operable to
generate a control signal that corresponds to the amount of coolant that
is presented to the conditioning device in response to the first signal.

4. The system of claim 3 further comprising a valve coupled between the
outlet of the fuel cell stack and the conditioning device and adapted to
control the amount of coolant presented to the conditioning device in
response to the control signal.

5. The system of claim 4 wherein the controller controls the valve to
increase the amount of coolant that is presented to the conditioning
device in response to the controller determining that the first
temperature is less than the predetermined temperature.

6. The system of claim 4 wherein the fuel cell stack is adapted to
transmit the temperature of the coolant to the controller, and the
controller controls the valve to decrease the amount of coolant that is
presented to the conditioning device in response to the controller
determining that the first temperature is greater than the predetermined
temperature and that the first temperature is less than the temperature
of the coolant.

7. The system of claim 1 wherein the conditioning device further comprises
an outer shell having first and second ends and the outer shell defining
a cavity therein, and at least one pipe extending through the cavity and
between the ends to enclose and deliver the fluid stream from the system
module to the fuel cell stack.

8. The system of claim 7 wherein the conditioning device further comprises
input and output ports and the fuel cell stack delivers coolant from the
outlet of the fuel cell stack through the input port and to the pipe to
change the first temperature of the fluid stream to be equal to the
predetermined temperature.

9. The system of claim 7 further comprising at least one humidity sensor
coupled to the outer shell.

10. The system of claim 9 wherein the at least one humidity sensor coupled
to the at least one pipe and exposed to the fluid stream to measure the
amount of water in the fluid stream.

11. The system of claim 7 comprising at least one temperature sensor
coupled to the pipe and exposed to the fluid stream to measure the first
temperature.

12. A method for conditioning the temperature of at least one fluid stream
that is passed through a fuel cell stack, the method
comprising:humidifying the fluid stream to a predetermined humidity level
upstream from the fuel cell stack and the predetermined humidity level
corresponds to a predetermined temperature having a specified
range;receiving the fluid stream at a first temperature that is different
from the predetermined temperature at one or more inlets of the fuel cell
stack;delivering coolant having a temperature that is different from the
predetermined temperature from at least one outlet of the fuel cell
stack; andpresenting the coolant to the fluid stream to adjust the first
temperature so that the first temperature is equal to the predetermined
temperature or within the specified range of the predetermined
temperature; andreceiving the fluid stream at the inlet of the fuel cell
stack at the predetermined temperature or within the specified range of
the predetermined temperature.

13. The method of claim 12 further comprising measuring the first
temperature of the fluid stream.

14. The method of claim 13 further comprising increasing the amount of
coolant that is presented to the fluid stream in response to determining
that the first temperature of the fluid stream is less than the
predetermined temperature.

15. The method of claim 15 further comprising decreasing the amount of
coolant that is presented to the fluid stream in response to determining
that the first temperature of the fluid stream is greater than the
predetermined temperature.

16. A conditioning device for conditioning the temperature of at least one
fluid stream to reach a predetermined temperature that is passed through
a fuel cell stack, the conditioning device comprising:an outer shell
having first and second ends and defining a cavity therein;at least one
pipe extending through the cavity and between the ends to enclose and
deliver the fluid stream to the fuel cell stack at a first temperature;at
least one input port disposed at the second end to receive coolant from
the fuel cell stack and present the coolant to the pipe to change the
first temperature of the fluid stream to be equal to the predetermined
temperature or within a specified range of the predetermined temperature;
andat least one output port disposed at the first end to deliver the
coolant away from the conditioning device.

17. The conditioning device of claim 16 further comprising at least one
humidity sensor coupled to the outer shell.

18. The conditioning device of claim 17 wherein the humidity sensor is
coupled to the pipe and exposed to the fluid stream to measure the amount
of water in the fluid stream.

19. The conditioning device of claim 16 further comprising at least one
temperature sensor disposed on the outer shell.

20. The conditioning device of claim 19 wherein the temperature sensor is
coupled to the tube and exposed to the fluid stream to measure the first
temperature.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]Embodiments of the present invention generally relate to a system
and method for conditioning the temperature of at least one fluid stream
that is passed through a fuel cell stack.

[0003]2. Background Art

[0004]It is generally well known that a number of fuel cells are joined
together to form a fuel cell stack. Such a stack generally provides
electrical power in response to electrochemically converting hydrogen and
oxygen. It is also generally well know that membranes of each fuel cell
are kept moist to facilitate performance and to prevent damage.
Conventional systems deliver water in the air and hydrogen streams to
ensure that such membranes are kept moist. While it is important to
ensure that membranes are kept moist, too much water particularly in the
liquid phase, in the air and hydrogen streams may lead to inefficient
operation of the fuel cells in the stack.

[0005]Liquid water may be delivered to the membranes or inlets of the fuel
cell stack if the air and hydrogen streams experience temperature loss
prior to being delivered to the fuel cell stack. The membranes of the
fuel cell stack may experience a shortage of water if the temperature of
the air and hydrogen streams increase prior to being delivered to the
fuel cell stack.

[0006]Accordingly, it would be desirable to provide a system and a method
for conditioning the temperature of the hydrogen and air streams that are
delivered to the fuel cell stack.

SUMMARY OF THE INVENTION

[0007]In one non-limiting embodiment, a system for conditioning the
temperature of at least one fluid stream that is passed through a fuel
cell stack is provided. The system comprises a system module, at least
one inlet and a conditioning device. The system module is disposed
upstream of the fuel cell stack and is operable to humidify the fluid
stream so that the fluid stream reaches a predetermined humidity level
and the predetermined humidity level corresponds to a predetermined
temperature. The one inlet of the fuel cell stack is adapted to receive
the fluid stream at a first temperature that is different from the
predetermined temperature. The fuel cell stack includes at least one
outlet that is operable to present coolant at a temperature that is
different from the first temperature of the fluid stream in response to
receiving the fluid stream. The conditioning device is operable to
receive the fluid stream and the coolant and present the coolant to the
fluid stream to change the first temperature of the fluid stream to be
equal to the predetermined temperature so that the inlet of the fuel cell
stack receives the fluid stream at the predetermined temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 illustrates an exemplary fuel cell stack humidity control and
conditioning system in accordance with one embodiment of the present
invention;

[0009]FIG. 2 illustrates a first side view of a conditioning device in
accordance with one embodiment of the present invention;

[0010]FIG. 3 illustrates a second side view of the conditioning device in
accordance with one embodiment of the present invention; and

[0011]FIG. 4 illustrates an elevated view of the conditioning device in
accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0012]FIG. 1 illustrates an exemplary fuel cell stack humidity control and
conditioning system 100 in accordance to one embodiment of the present
invention. The system 100 may be implemented in an electric vehicle or
hybrid vehicle or any such vehicle which uses voltage to drive a motor.
The system generally comprises a system module 102, a controller 104, a
conditioning device 106 and a fuel cell stack 108.

[0013]The system module 102 generates first and second fluid streams for
the system 100. The first fluid stream which comprises air is fed to a
mass airflow sensor 110. The air passing through the mass airflow sensor
110 may be dry air, or it may have a high water content. The mass airflow
sensor 110 measures the amount and density of air in the fluid stream. An
air compressor 112 pressurizes the air stream.

[0014]The system module 102 comprises a first humidifier arrangement 114
configured to add water in the air stream. The first humidifier
arrangement 114 includes a water injector 116 and a humidifier 118. In
one example, the first humidifier arrangement 114 may be implemented as a
gas-to-gas humidifier. The particular type of humidifier arrangement used
may be varied to meet the design criteria of a particular implementation.
The controller 104 may control the water injector 116 with a first pulse
width modulated (PWM) signal. The water injector 116 may be implemented
as a solenoid or other valve and control the amount of water that is
being added to humidifier 118 in response to the first PWM signal.

[0015]In one example not shown, the water injector valve 116 may be
positioned between the mass airflow sensor 110 and the air compressor
112. In such an example, the water injection valve 116 may inject water
directly into the compressor 112 and the humidifier 118 may be eliminated
from the system 100.

[0016]The system module 102 comprises a water reservoir 122 and a water
pump 124. The water pump 124 is coupled to the water injector 116. The
water reservoir 122 provides water to the water injector 116 via the
water pump 124. In one example, the fuel cell stack 108 may provide a
water supply to the water reservoir 122. For example, the fuel cell stack
108 may generate water in response to combining chemicals from the air
and hydrogen streams.

[0017]The system module 102 includes a tank 130 of compressed hydrogen
which provides a second fluid stream. The second fluid stream comprises
compressed hydrogen that can be used by the fuel cell stack 108. While
compressed hydrogen may be used in the system 100, any hydrogen fuel
source may be implemented in the system 100. For example, liquid
hydrogen, hydrogen stored in various chemicals such as sodium borohydride
or alanates, or hydrogen stored in metal hybrids may be used instead of
compressed gas. A tank valve 131 controls the flow of hydrogen entering
into the system 100. A pressure regulator 132 regulates the flow of the
hydrogen. The hydrogen passing through the pressure regulator 132 may be
dry hydrogen, or it may have a high water content. A second humidifier
arrangement 134 is configured to add water into the hydrogen stream.

[0018]The second humidifier arrangement 134 includes a water injector 140
and a humidifier 142. In one example, the second humidifier arrangement
134 may be implemented as a gas-to-gas humidifier. The particular type of
humidifier arrangement used may be varied to meet the design criteria of
a particular implementation. The controller 104 may control the water
injector 140 with a second PWM signal. The water injector 140 may be
implemented as a solenoid or other valve and control the amount of water
that is being added to humidifier 118 in response to the second PWM
signal. The humidifier 142 introduces water into the hydrogen stream in
response to the amount of water received by the water injector 140. The
water pump 124 is coupled to the water injector 140. The water reservoir
122 provides water to the water injector 140 via the water pump 124.

[0019]The conditioning device 106 comprises a first sensor 144 configured
to measure the dew point in the air stream. In one example, the first
sensor 144 may be implemented as a capacitive complementary metal oxide
semiconductor (CMOS) sensing element. The dew point is generally a
function of relative humidity and temperature. The first sensor 144 may
be adapted to measure any number of characteristics related to
determining the amount of water in the air. The conditioning device 106
further comprises a temperature sensor 146. The temperature sensor 146
measures the temperature of the air stream. A first inlet 148 of the fuel
cell stack 108 may receive the humidified air.

[0020]The conditioning device further comprises a second sensor 150
configured to measure the dew point in the hydrogen stream. The second
sensor 150 may be implemented as a CMOS sensing element. The second
sensor 150 may be adapted to measure any number of characteristics
related to the amount of water in the hydrogen stream. A temperature
sensor 152 measures the temperature of the hydrogen. A second inlet 154
of the fuel cell stack 108 may receive the humidified hydrogen stream.

[0021]The fuel cell stack 108 generally comprises a number of fuel cells
(not shown) for generating power to drive a motor. In general, each fuel
cell electrochemically converts oxygen from the air stream and hydrogen
from the hydrogen stream to produce electricity and water. Membranes (not
shown) facilitate the process of electrochemically converting oxygen and
hydrogen to produce electricity and water. The fuel cell stack 108
generates stack current in response to each fuel cell converting oxygen
and hydrogen into electricity and water. Such stack current may drive an
electric motor (not shown) coupled to the fuel cell stack 108. The fuel
cell stack 108 may provide information related to the stack current to
the controller 120 via a current sensor (not shown). The fuel cell stack
108 comprises first, second and third outlets 156, 158 and 160. The first
outlet 156 presents water and air generated from combining hydrogen and
oxygen from the fuel cell stack 108. The second outlet 158 presents
hydrogen from the fuel cell stack 108. The third outlet 160 presents
coolant in the form of de-ionized (DI) water ethylene glycol or other
suitable coolant from the fuel cell stack 108 in response to combining
hydrogen with oxygen (e.g., from the air stream).

[0022]The conditioning device 106 comprises an input port 162 and an
output port 164. The conditioning device 106 may be adapted to include
two or more input or output ports. The number of input and output ports
may be varied based on the design criteria of a particular
implementation. A valve 166 may be adapted to control the amount of
coolant that is delivered to the input port 162 of the conditioning
device 106. A cooling module 168 (which is part of the vehicle heating
and cooling system) is adapted to receive coolant from the output port
164 of the conditioning device 106 or the valve 166. An inlet 153 of the
fuel cell stack 108 is adapted to receive the coolant from the cooling
module 168. The cooling module 168 also presents coolant to the
humidifiers 118 and 142.

[0023]In operation, the system 100 is adapted to ensure the proper levels
of humidity in the air and hydrogen streams are delivered to the inlets
148, 154 to ensure proper operation of the membranes in the fuel cells in
the fuel cell stack 108. In connection with the air stream, the
controller 104 is adapted to control the humidifier arrangement 114 to
deliver water to the air stream such that the air stream reaches a
predetermined humidity level. The humidifier 118 is adapted to measure
and present the amount of water in the air stream to the controller 104
thereby establishing a closed loop system with the controller 104. As
noted above, the controller 104 controls the water injector 116 to
dispense the corresponding amount of water into the humidifier 118. The
humidifier 118 heats the water and releases a warm stream into the air
stream thereby increasing the temperature of the air stream. The
humidifier 118 may also cool the incoming air stream based on the
temperature of the air stream at an outlet of the air compressor 112. The
temperature of the air stream may also be based on the amount of
compression of the air in the air compressor 112 and the temperature
coolant presented to the humidifier 118 from the cooling module 168.

[0024]Once the predetermined humidity level of the air stream has been
achieved, the corresponding temperature of the air stream at the
predetermined humidity level is defined as the predetermined temperature.
In one example, the predetermined humidity level may be established as
disclosed in co-pending U.S. Application Ser. No. ______, filed on
______, 2007, entitled "Fuel Cell Humidity Control System and Method,"
Attorney's Docket No. 81150538, which is hereby incorporated in its
entirety by reference. In another example, the controller 104 may use
look up tables (stored in the controller 104) to determine the
predetermined humidity level. In another example, the predetermined
humidity level may be based on the temperature of the coolant at the
inlet 153 of the fuel cell stack 108. The fuel cell stack 108 is
configured to present the temperature of the coolant at the inlet 153 to
the controller 104. The implementations as set forth for establishing the
predetermined humidity level in the air stream also apply to the hydrogen
stream.

[0025]In general, the predetermined humidity level of the air stream is
the amount of water that is in the air stream that is sufficient to
ensure proper operation of the membranes in the fuel cells in the fuel
cell stack 108. In one example, due to the physical displacement between
the system module 102 and the fuel cell stack 108 (or from other
conditions that may exist in the system 100 that may reduce/increase the
predetermined temperature to a first temperature), the air stream may
encounter heat loss or gain which changes the temperature of the air
stream from the predetermined temperature to the first temperature.

[0026]If the controller 104 determines that the first temperature is less
than the predetermined temperature, then the controller 104 controls the
valve 166 to allow for an increased amount of coolant to be delivered to
the input port 162 of the conditioning device 106. The air stream is
enclosed within a tube (not shown in FIG. 1) of the conditioning device
106 and is exposed to the heat of the coolant to increase the first
temperature of the air stream to reach the predetermined temperature, or
a temperature that is within a specified range of the predetermined
temperature. The specified range may vary based on fuel cell stack
requirements. For example, different fuel cell stacks may output coolant
at different temperature levels during various operational modes of the
vehicle thereby affecting the temperature of the coolant.

[0027]By maintaining the air stream at the predetermined temperature, or
within the specified range, the system 100 is able to maintain the
relative humidity target (e.g. based on the predetermined humidity level)
as established via the controller 104 for the membranes. The fuel cell
stack 108 is configured to present the temperature of the coolant to the
controller 104.

[0028]If the controller 104 determines that the first temperature is
greater than the predetermined temperature, then the controller 104
controls the valve 166 to decrease or stop the flow of coolant to the
input port 162 of the conditioning device 106. The air stream is enclosed
within a tube (not shown in FIG. 1) of the conditioning device 106 and is
exposed to no coolant or a lesser amount of coolant to allow the first
temperature to reach the predetermined temperature.

[0029]In connection with the hydrogen stream, the controller 104 is
adapted to control the humidifier arrangement 134 to control the amount
of water that is added to the hydrogen stream such that the hydrogen
stream reaches a predetermined humidity level. The humidifier 142 is
adapted to measure and present the amount of water in the hydrogen stream
to the controller 104 thereby establishing a closed loop system with the
controller 104. As noted above, the controller 104 controls the water
injector 140 to dispense the corresponding amount of water into the
humidifier 142. The humidifier 142 heats the water and releases a warm
stream into the hydrogen stream thereby increasing the temperature of the
hydrogen stream. The humidifier 142 may also cool the hydrogen streams.
As noted in connection with the heating of the air stream, the
recirculation of the coolant from the cooling module 168 to the
humidifier 142 provides a heat source to heat the hydrogen stream.

[0030]Once the predetermined humidity level of the hydrogen stream has
been achieved, the corresponding temperature of the hydrogen stream at
the predetermined humidity level is defined as the predetermined
temperature. In general, the predetermined humidity level of the hydrogen
stream is the amount of water that is in the hydrogen stream that is
sufficient to ensure proper operation of the membranes in the fuel cells
in the fuel cell stack 108. In one example, due to the physical
displacement between the system module 102 and the fuel cell stack 108
(or from other conditions that may exist in the system 100 that may
reduce/increase the predetermined temperature to the first temperature),
the predetermined temperature of the hydrogen stream may encounter heat
loss which changes the temperature of the hydrogen stream from the
predetermined temperature to a first temperature.

[0031]If the controller 104 determines that the first temperature is less
than the predetermined temperature, then the controller 104 controls the
valve 166 to allow for an increased amount of coolant to be delivered to
the input port 162 of the conditioning device 106. The hydrogen stream is
enclosed within a tube of the conditioning device 106 and is exposed to
the heat of the coolant to increase the first temperature of the hydrogen
stream to reach the predetermined temperature. By maintaining the
hydrogen stream at the predetermined temperature, the system 100 is able
to maintain the relative humidity target (e.g. based on the predetermined
humidity level) as established via the controller 104 for the membranes.

[0032]If the controller 104 determines that the first temperature is
greater than the predetermined temperature, then the controller 104
controls the valve 166 to decrease or stop the flow of coolant to the
input port 162 of the conditioning device 106. The hydrogen stream is
enclosed within a tube (not shown) of the conditioning device 106 and is
exposed to no coolant or a lesser amount of coolant to allow the first
temperature to reach the predetermined temperature.

[0033]While FIG. 1 illustrates the conditioning device 106 being
implemented outside of the fuel cell stack 108, the fuel cell stack 108
may be adapted to include conditioning device 106. With such an
implementation, the conditioning device 106 may ensure that the
predetermined humidity level of the air and gas streams are achieved
prior to the streams reaching the fuel cells (not shown) of the fuel cell
stack 106.

[0034]FIGS. 2-4 illustrates various views of the conditioning device 106.
The conditioning device 106 comprises an outer shell 200. The outer shell
200 includes a first end 202 orientated toward the system module 102 and
a second end 204 orientated toward the fuel cell stack interface (or the
inlets 148, 154 of the fuel cell stack 108). The outer shell 200 includes
a cavity 206. A first pipe 208 is disposed within the outer shell 200 and
extends through the cavity 206 and out of the ends 202, 204. The first
pipe 208 delivers the hydrogen stream from the system module 102 to the
fuel cell stack 108. A second pipe 210 is disposed within the outer shell
200 and extends through the cavity 206 and out of the ends 202, 204. The
second pipe 210 delivers the air stream from the system module 102 to the
fuel cell stack 108.

[0035]The input port 162 is disposed at the second end 204 of the outer
shell 200. The output port 164 is disposed at the first end 202 of the
outer shell 200. The input port 162 is coupled to the outlet 160 of the
fuel cell stack 108 and adapted to receive coolant from the fuel cell
stack 108. The coolant is passed over the first and second pipes 208, 210
to heat the air and hydrogen streams to the predetermined temperature.
The output port 164 delivers coolant away from the conditioning device
106 and to the cooling module 168.

[0036]The first and second sensors 144, 150 are coupled to the outer shell
200 and to the first and second pipes 208, 210 respectively. The first
and second sensors 144, 150 are exposed to the air and hydrogen streams
to measure the amount of water in the streams. The temperature sensors
146, 152 are coupled to the first and second sensors 144, 150
respectively.

[0037]In one embodiment, the conditioning device 106 may be packaged
within the fuel cell stack 108. In addition, the conditioning device 106
may be implemented without the first and second sensors 144, 150 and the
temperature sensors 146, 152 to allow for an open loop system such that
the conditioning device 106 applies coolant to the air and hydrogen
streams to increase the temperatures of the air and hydrogen streams to
compensate for any heat losses that occur with the delivery of the air
and hydrogen streams to the fuel cell stack.

[0038]While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this invention
relates will recognize various alternative designs and embodiments for
practicing the invention as defined by the following claims.